/*
 * Copyright 2017 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkHighContrastFilter_DEFINED
#define SkHighContrastFilter_DEFINED

#include "include/core/SkRefCnt.h"
#include "include/core/SkScalar.h"
#include "include/core/SkTypes.h"

class SkColorFilter;

/* *
 * Configuration struct for SkHighContrastFilter.
 *
 * Provides transformations to improve contrast for users with low vision.
 */
struct SkHighContrastConfig {
    enum class InvertStyle {
        kNoInvert,
        kInvertBrightness,
        kInvertLightness,

        kLast = kInvertLightness
    };

    SkHighContrastConfig()
    {
        fGrayscale = false;
        fInvertStyle = InvertStyle::kNoInvert;
        fContrast = 0.0f;
    }

    SkHighContrastConfig(bool grayscale, InvertStyle invertStyle, SkScalar contrast)
        : fGrayscale(grayscale), fInvertStyle(invertStyle), fContrast(contrast)
    {}

    // Returns true if all of the fields are set within the valid range.
    bool isValid() const
    {
        return fInvertStyle >= InvertStyle::kNoInvert && fInvertStyle <= InvertStyle::kInvertLightness &&
            fContrast >= -1.0 && fContrast <= 1.0;
    }

    // If true, the color will be converted to grayscale.
    bool fGrayscale;

    // Whether to invert brightness, lightness, or neither.
    InvertStyle fInvertStyle;

    // After grayscale and inverting, the contrast can be adjusted linearly.
    // The valid range is -1.0 through 1.0, where 0.0 is no adjustment.
    SkScalar fContrast;
};

/* *
 * Color filter that provides transformations to improve contrast
 * for users with low vision.
 *
 * Applies the following transformations in this order. Each of these
 * can be configured using SkHighContrastConfig.
 *
 * - Conversion to grayscale
 * - Color inversion (either in RGB or HSL space)
 * - Increasing the resulting contrast.
 *
 * Calling SkHighContrastFilter::Make will return nullptr if the config is
 * not valid, e.g. if you try to call it with a contrast outside the range of
 * -1.0 to 1.0.
 */

struct SK_API SkHighContrastFilter {
    // Returns the filter, or nullptr if the config is invalid.
    static sk_sp<SkColorFilter> Make(const SkHighContrastConfig &config);
};

#endif
